TURBINE ENGINES TURBINE ENGINES TURBINE ENGINES TURBINE ENGINES COMPRESSOR TYPES COMPRESSOR TYPES COMPRESSOR TYPES COMPRESSOR TYPES (FAA AC 65 (FAA AC 65 (FAA AC 65 (FAA AC 65-12A 12A 12A 12A - Powerplant Handbook) Powerplant Handbook) Powerplant Handbook) Powerplant Handbook) ~ The two principal types of compressors currently being used in gas turbine aircraft engines are centrifugal flow and axial flow. ~ Much use has been made of the terms "centrifugal flow" and "axial flow" to describe the complete engine. However, the terms are applicable only to the flow of air through the compressor. ~ In the centrifugal-flow engine, the compressor achieves its purpose by picking up the entering air and accelerating it outwardly by centrifugal action. A single stage delivers a pressure ratio of around 5:1 & and a two stage around 8:1. Design of the more modern centrifugal compressors sees them approaching pressure ratios of 15:1. ~ In the axial-flow engine, the air is compressed while continuing in its original direction of flow, thus avoiding the energy loss caused by turns. From inlet to exit the air flows along an axial path and is compressed at a ratio of approximately 1.25:1 per stage. The centrifugal The centrifugal The centrifugal The centrifugal-flow comp flow comp flow comp flow compressor's advantages are: ressor's advantages are: ressor's advantages are: ressor's advantages are: (1) High pressure rise per stage (2) Good efficiencies over wide rotational speed range (3) Simplicity of manufacture, thus low cost (4) Low weight (5) Low starting power requirements The centrifugal The centrifugal The centrifugal The centrifugal-flow compressor's disadvantage flow compressor's disadvantage flow compressor's disadvantage flow compressor's disadvantages are: s are: s are: s are: (1) Large frontal area for given airflow (2) More than two stages are not practical because of losses in turns between stages The axial The axial The axial The axial-flow compressor's advantages are: flow compressor's advantages are: flow compressor's advantages are: flow compressor's advantages are: (1) High peak efficiencies (2) Small frontal area for given airflow (3) Straight-through flow, allowing high ram efficiency (4) Increased pressure rise by increasing number of stages with negligible losses The axial The axial The axial The axial-flow compressor's disadvantages are: flow compressor's disadvantages are: flow compressor's disadvantages are: flow compressor's disadvantages are: (1) Good efficiencies over only narrow rotational speed range (2) Difficulty of manufacture and high cost (3) Relatively high weight (4) High starting power requirements (this has been partially overcome by multi-spool compressors) ~ From an analysis of the centrifugal and axial flow engine compressors at their present stage of development, the axial-flow type has definite advantages. Also, the advent of the split-spool axial compressor has made these advantages even more positive by offering greater starting flexibility and improved high-altitude performance.
TURBINE ENGINESTURBINE ENGINESTURBINE ENGINESTURBINE ENGINES
COMPRESSOR TYPESCOMPRESSOR TYPESCOMPRESSOR TYPESCOMPRESSOR TYPES
(FAA AC 65(FAA AC 65(FAA AC 65(FAA AC 65----12A 12A 12A 12A ----
Powerplant Handbook)Powerplant Handbook)Powerplant
Handbook)Powerplant Handbook) ~ The two principal types of
compressors currently being used in gas turbine aircraft engines
are centrifugal flow and axial flow. ~ Much use has been made of
the terms "centrifugal flow" and "axial flow" to describe the
complete engine. However, the terms are applicable only to the flow
of air through the compressor. ~ In the centrifugal-flow engine,
the compressor achieves its purpose by picking up the entering air
and accelerating it outwardly by centrifugal action. A single stage
delivers a pressure ratio of around 5:1 & and a two stage
around 8:1. Design of the more modern centrifugal compressors sees
them approaching pressure ratios of 15:1. ~ In the axial-flow
engine, the air is compressed while continuing in its original
direction of flow, thus avoiding the energy loss caused by turns.
From inlet to exit the air flows along an axial path and is
compressed at a ratio of approximately 1.25:1 per stage. The
centrifugalThe centrifugalThe centrifugalThe centrifugal----flow
compflow compflow compflow compressor's advantages are:ressor's
advantages are:ressor's advantages are:ressor's advantages are: (1)
High pressure rise per stage (2) Good efficiencies over wide
rotational speed range (3) Simplicity of manufacture, thus low cost
(4) Low weight (5) Low starting power requirements The
centrifugalThe centrifugalThe centrifugalThe centrifugal----flow
compressor's disadvantageflow compressor's disadvantageflow
compressor's disadvantageflow compressor's disadvantages are:s
are:s are:s are: (1) Large frontal area for given airflow (2) More
than two stages are not practical because of losses in turns
between stages The axialThe axialThe axialThe axial----flow
compressor's advantages are:flow compressor's advantages are:flow
compressor's advantages are:flow compressor's advantages are: (1)
High peak efficiencies
(2) Small frontal area for given airflow
(3) Straight-through flow, allowing high ram efficiency
(4) Increased pressure rise by increasing number of stages with
negligible losses
The axialThe axialThe axialThe axial----flow compressor's
disadvantages are:flow compressor's disadvantages are:flow
compressor's disadvantages are:flow compressor's disadvantages are:
(1) Good efficiencies over only narrow rotational speed range (2)
Difficulty of manufacture and high cost (3) Relatively high weight
(4) High starting power requirements (this has been partially
overcome by multi-spool compressors) ~ From an analysis of the
centrifugal and axial flow engine compressors at their present
stage of development, the axial-flow type has definite advantages.
Also, the advent of the split-spool axial compressor has made these
advantages even more positive by offering greater starting
flexibility and improved high-altitude performance.
